A person who is into all things motorized. This can be cars, motorcycles, machines, planes, or boats, but specifically relating to the engine and power delivery. Knowing how to weld and machine metal are also traits of a gearhead.

Dude, she's such a gearhead. Go show her that old lathe and tools in your grandfather's garage and she'll be in heaven.

A musician (most common in guitarists and drummers) who spends more time reading about and buying gear than they actually spend playing music. Gear heads think that by spitting out a flood of brand names and model numbers to their friends that they will sound more intelligent than they actually are. Also, they hope their new equipment will compensate for their lack of practice. Truthfully it shows they spend too much time on the toilet reading "Musicians Friend".